import { limitAsync } from './limitAsync.ts';

interface MapAsyncOptions {
  concurrency?: number;
}

/**
 * Transforms each element in an array using an async callback function and returns
 * a promise that resolves to an array of transformed values.
 *
 * @template T - The type of elements in the input array.
 * @template R - The type of elements in the output array.
 * @param {readonly T[]} array The array to transform.
 * @param {(item: T, index: number, array: readonly T[]) => Promise<R>} callback An async function that transforms each element.
 * @param {MapAsyncOptions} [options] Optional configuration object.
 * @param {number} [options.concurrency] Maximum number of concurrent async operations. If not specified, all operations run concurrently.
 * @returns {Promise<R[]>} A promise that resolves to an array of transformed values.
 * @example
 * const users = [{ id: 1 }, { id: 2 }, { id: 3 }];
 * const userDetails = await mapAsync(users, async (user) => {
 *   return await fetchUserDetails(user.id);
 * });
 * // Returns: [{ id: 1, name: '...' }, { id: 2, name: '...' }, { id: 3, name: '...' }]
 *
 * @example
 * // With concurrency limit
 * const numbers = [1, 2, 3, 4, 5];
 * const results = await mapAsync(
 *   numbers,
 *   async (n) => await slowOperation(n),
 *   { concurrency: 2 }
 * );
 * // Processes at most 2 operations concurrently
 */
export function mapAsync<T, R>(
  array: readonly T[],
  callback: (item: T, index: number, array: readonly T[]) => Promise<R>,
  options?: MapAsyncOptions
): Promise<R[]> {
  if (options?.concurrency != null) {
    callback = limitAsync(callback, options.concurrency);
  }

  return Promise.all(array.map(callback));
}
